1. Field
The present invention relates generally to energy storage devices, such as supercapacitors and lithium ion batteries, for fast charging and operation at high rate at very low temperatures, more particularly to methods and apparatus for fast charging of energy storage devices, such as supercapacitors and lithium ion batteries and to supercapacitors and lithium ion batteries that are designed to be charged at high rates as well as for high discharge rate operation at very low temperatures. Herein, by very low temperature it is meant the temperatures at which an electrolyte in an interior of such energy storage devices at least hinders charging, such as at temperatures where the electrolyte becomes nearly solid, usually around −45 degrees C., but as low as −54 degrees C. or below.
2. Prior Art
A supercapacitor (SC), sometimes referred to as an ultra capacitor, and formerly referred to as an electric double-layer capacitor (EDLC) is a high-capacity electrochemical capacitor with capacitance values up to 10,000 Farads at 1.2 volt that bridge the gap between electrolytic capacitors and rechargeable batteries (each of which are collectively referred to herein as a “supercapacitor”). Such supercapacitors typically store 10 to 100 times more energy per unit volume or mass than electrolytic capacitors, can accept and deliver charge much faster than batteries, and tolerate many more charge and discharge cycles than rechargeable batteries. They are however around 10 times larger than conventional batteries for a given charge. The construction and properties of many different types of supercapacitors are well known in the art.
In certain applications, such as in munitions, supercapacitors may be required to be charged as well as discharge at very low temperatures, sometimes as low as −40 to −65 degrees F. or even lower. Similar very low charging and operating temperatures may also be faced in many commercial applications, such is in supercapacitors used in vehicles for direct powering or for regeneration circuits used during braking. At such very low temperatures, the supercapacitor electrolyte becomes solid, thereby hampering or preventing ion transportation within the electrolyte. As a result, the supercapacitor rate of charge and discharge is greatly diminished. As a result, the user may be unable to charge or when the temperature levels are not very low and the supercapacitor is not provided with enough thermal insulation protection, must wait a relatively long time to charge the supercapacitor. It is appreciated by those skilled in the art that this is the case for all currently available supercapacitors.
Similarly, charging methods and devices for currently available rechargeable batteries, such as lithium ion batteries, cannot be used for charging these batteries at low temperatures. Although applicable to any rechargeable battery having an electrolyte interior, reference below will be made to lithium ion batteries by way of example. However, such low temperatures with regard to lithium ion batteries can be much higher than that discussed above with regard to supercapacitors, such as close to zero degrees C., and still hinder charging, damage the battery and even cause fire hazard because the components of a lithium ion battery are highly sensitive to temperature. At low temperature, the “viscous” resistance of the electrolyte to the movement of lithium ions increases. This increase in resistance causes higher losses during charging and discharging of the lithium ion battery. Low temperature charging passes (relatively high) currents through the components representing the battery electrical-chemical reactions, and is well known to result in so-called lithium plating, which is essentially irreversible, prevents battery charging, and permanently damages the battery.